While it is well known to utilize reinforcing elements including various types of fibers to provide increased strength in paper products, the known fibrous materials do not impart much in the way of structural strength, nor do they add much rigidity and stiffness to the finished product. In the case of corrugated board, which is made with various weights of paper, increased stiffness and strength have been obtained by increasing the weight of the paper utilized for both the corrugated central medium as well as the overlying layers or facings. In fact, when heavy packing cases were to be made of corrugated board, several layers of corrugated board had to be laminated in order to obtain the desired stiffness and strength. It is well known that corrugated board has been manufactured for many decades, yet the only procedures that have been considered economical and practical to obtain increased structural strength and stiffness have involved the use of paper of increased weight, and the lamination of layers of corrugated board. It is well recognized however that notwithstanding the utilization of heavier paper, and also the lamination of corrugated board the resulting product is still subject to adverse effects of moisture which results in substantial softening of the board and loss of the protection intended to be afforded by it.
In copending application Ser. No. 599,142, filed July 25, 1975, now U.S. Pat. No. 4,203,790, for "Reinforced Paper Products and Method and Apparatus for the Manufacturing Thereof", there is disclosed an improved wire reinforced corrugated board and other products in which the corrugated medium for corrugated board is comprised of a plurality of wires adhered in contact to a paper web which is then corrugated transversely of the wires so that the wires and the paper conform to one another. This corrugated medium then has outer paper layers or liners adhered to the crest portions of each side of the corrugating medium to form a double faced wire reinforced corrugated board. The plurality of wire elements in the corrugating medium provide improved rigidity and strength for the resulting corrugated board. In particular, the compressive or bending forces applied to the corrugated board may be greatly increased as a result of the triangular truss structure formed by the wire elements in the corrugated medium of a double faced cardboard construction. That is, when compressive or bending forces are applied to the cardboard, the wire legs are placed into compression which is one of the strengths of wire. Thus, the structure will support substantial compressive forces.
Copending application Ser. No. 878,158, filed Feb. 15, 1978, now U.S. Pat. No. 4,232,074 for "Improved Reinforced Paper Products and Method for the Manufacturing Thereof" is directed to a further improvement in such wire reinforced corrugated board in which the plurality of wires are disposed in spaced parallel channels or trenches formed on one surface of a paper layer. The channels are of a depth and thickness substantially corresponding to the thickness of the wires disposed therein, and a second paper layer is adhesively secured over the channels to tightly hold the wires in place between two paper layers. In this manner, a smooth, flat, aesthetically pleasing outer surface for the resulting paper structure is obtained. In addition, the wires are firmly held in place so that they will not move or shift around during subsequent cutting and/or corrugation of the wire reinforced laminate in manufacturing corrugated cardboard. This is most advantageous, particularly when it is realized that the common adhesives used in the corrugated industry have generally comprised water-based emulsion adhesives which have been totally satisfactory in firmly adhering the wires in place between or to the outer paper layers. Thus, the channels serve an important function in preventing the shifting or movement of the wires which is most advantageous in maintaining the integrity of the overall product, as well as maintaining safety in handling and manufacture thereof.